/* ----------------------------------------------------------------------
* Copyright (C) 2010 ARM Limited. All rights reserved.
*
* $Date:        15. February 2012
* $Revision: 	V1.1.0
*
* Project: 	    CMSIS DSP Library
* Title:	    arm_iir_lattice_q31.c
*
* Description:	Q31 IIR lattice filter processing function.
*
* Target Processor: Cortex-M4/Cortex-M3/Cortex-M0
*
* Version 1.1.0 2012/02/15
*    Updated with more optimizations, bug fixes and minor API changes.
*
* Version 1.0.10 2011/7/15
*    Big Endian support added and Merged M0 and M3/M4 Source code.
*
* Version 1.0.3 2010/11/29
*    Re-organized the CMSIS folders and updated documentation.
*
* Version 1.0.2 2010/11/11
*    Documentation updated.
*
* Version 1.0.1 2010/10/05
*    Production release and review comments incorporated.
*
* Version 1.0.0 2010/09/20
*    Production release and review comments incorporated
*
* Version 0.0.7  2010/06/10
*    Misra-C changes done
* -------------------------------------------------------------------- */

#include "arm_math.h"

/**
 * @ingroup groupFilters
 */

/**
 * @addtogroup IIR_Lattice
 * @{
 */

/**
 * @brief Processing function for the Q31 IIR lattice filter.
 * @param[in] *S points to an instance of the Q31 IIR lattice structure.
 * @param[in] *pSrc points to the block of input data.
 * @param[out] *pDst points to the block of output data.
 * @param[in] blockSize number of samples to process.
 * @return none.
 *
 * @details
 * <b>Scaling and Overflow Behavior:</b>
 * \par
 * The function is implemented using an internal 64-bit accumulator.
 * The accumulator has a 2.62 format and maintains full precision of the intermediate multiplication results but provides only a single guard bit.
 * Thus, if the accumulator result overflows it wraps around rather than clip.
 * In order to avoid overflows completely the input signal must be scaled down by 2*log2(numStages) bits.
 * After all multiply-accumulates are performed, the 2.62 accumulator is saturated to 1.32 format and then truncated to 1.31 format.
 */

void arm_iir_lattice_q31(
    const arm_iir_lattice_instance_q31* S,
    q31_t* pSrc,
    q31_t* pDst,
    uint32_t blockSize)
{
	q31_t fcurr, fnext = 0, gcurr = 0, gnext;      /* Temporary variables for lattice stages */
	q63_t acc;                                     /* Accumlator */
	uint32_t blkCnt, tapCnt;                       /* Temporary variables for counts */
	q31_t* px1, *px2, *pk, *pv;                    /* Temporary pointers for state and coef */
	uint32_t numStages = S->numStages;             /* number of stages */
	q31_t* pState;                                 /* State pointer */
	q31_t* pStateCurnt;                            /* State current pointer */

	blkCnt = blockSize;

	pState = &S->pState[0];


#ifndef ARM_MATH_CM0

	/* Run the below code for Cortex-M4 and Cortex-M3 */

	/* Sample processing */
	while(blkCnt > 0u) {
		/* Read Sample from input buffer */
		/* fN(n) = x(n) */
		fcurr = *pSrc++;

		/* Initialize state read pointer */
		px1 = pState;
		/* Initialize state write pointer */
		px2 = pState;
		/* Set accumulator to zero */
		acc = 0;
		/* Initialize Ladder coeff pointer */
		pv = &S->pvCoeffs[0];
		/* Initialize Reflection coeff pointer */
		pk = &S->pkCoeffs[0];


		/* Process sample for first tap */
		gcurr = *px1++;
		/* fN-1(n) = fN(n) - kN * gN-1(n-1) */
		fnext = __QSUB(fcurr, (q31_t)(((q63_t) gcurr * (*pk)) >> 31));
		/* gN(n) = kN * fN-1(n) + gN-1(n-1) */
		gnext = __QADD(gcurr, (q31_t)(((q63_t) fnext * (*pk++)) >> 31));
		/* write gN-1(n-1) into state for next sample processing */
		*px2++ = gnext;
		/* y(n) += gN(n) * vN  */
		acc += ((q63_t) gnext * *pv++);

		/* Update f values for next coefficient processing */
		fcurr = fnext;

		/* Loop unrolling.  Process 4 taps at a time. */
		tapCnt = (numStages - 1u) >> 2;

		while(tapCnt > 0u) {

			/* Process sample for 2nd, 6th .. taps */
			/* Read gN-2(n-1) from state buffer */
			gcurr = *px1++;
			/* fN-2(n) = fN-1(n) - kN-1 * gN-2(n-1) */
			fnext = __QSUB(fcurr, (q31_t)(((q63_t) gcurr * (*pk)) >> 31));
			/* gN-1(n) = kN-1 * fN-2(n) + gN-2(n-1) */
			gnext = __QADD(gcurr, (q31_t)(((q63_t) fnext * (*pk++)) >> 31));
			/* y(n) += gN-1(n) * vN-1  */
			/* process for gN-5(n) * vN-5, gN-9(n) * vN-9 ... */
			acc += ((q63_t) gnext * *pv++);
			/* write gN-1(n) into state for next sample processing */
			*px2++ = gnext;

			/* Process sample for 3nd, 7th ...taps */
			/* Read gN-3(n-1) from state buffer */
			gcurr = *px1++;
			/* Process sample for 3rd, 7th .. taps */
			/* fN-3(n) = fN-2(n) - kN-2 * gN-3(n-1) */
			fcurr = __QSUB(fnext, (q31_t)(((q63_t) gcurr * (*pk)) >> 31));
			/* gN-2(n) = kN-2 * fN-3(n) + gN-3(n-1) */
			gnext = __QADD(gcurr, (q31_t)(((q63_t) fcurr * (*pk++)) >> 31));
			/* y(n) += gN-2(n) * vN-2  */
			/* process for gN-6(n) * vN-6, gN-10(n) * vN-10 ... */
			acc += ((q63_t) gnext * *pv++);
			/* write gN-2(n) into state for next sample processing */
			*px2++ = gnext;


			/* Process sample for 4th, 8th ...taps */
			/* Read gN-4(n-1) from state buffer */
			gcurr = *px1++;
			/* Process sample for 4th, 8th .. taps */
			/* fN-4(n) = fN-3(n) - kN-3 * gN-4(n-1) */
			fnext = __QSUB(fcurr, (q31_t)(((q63_t) gcurr * (*pk)) >> 31));
			/* gN-3(n) = kN-3 * fN-4(n) + gN-4(n-1) */
			gnext = __QADD(gcurr, (q31_t)(((q63_t) fnext * (*pk++)) >> 31));
			/* y(n) += gN-3(n) * vN-3  */
			/* process for gN-7(n) * vN-7, gN-11(n) * vN-11 ... */
			acc += ((q63_t) gnext * *pv++);
			/* write gN-3(n) into state for next sample processing */
			*px2++ = gnext;


			/* Process sample for 5th, 9th ...taps */
			/* Read gN-5(n-1) from state buffer */
			gcurr = *px1++;
			/* Process sample for 5th, 9th .. taps */
			/* fN-5(n) = fN-4(n) - kN-4 * gN-1(n-1) */
			fcurr = __QSUB(fnext, (q31_t)(((q63_t) gcurr * (*pk)) >> 31));
			/* gN-4(n) = kN-4 * fN-5(n) + gN-5(n-1) */
			gnext = __QADD(gcurr, (q31_t)(((q63_t) fcurr * (*pk++)) >> 31));
			/* y(n) += gN-4(n) * vN-4  */
			/* process for gN-8(n) * vN-8, gN-12(n) * vN-12 ... */
			acc += ((q63_t) gnext * *pv++);
			/* write gN-4(n) into state for next sample processing */
			*px2++ = gnext;

			tapCnt--;

		}

		fnext = fcurr;

		/* If the filter length is not a multiple of 4, compute the remaining filter taps */
		tapCnt = (numStages - 1u) % 0x4u;

		while(tapCnt > 0u) {
			gcurr = *px1++;
			/* Process sample for last taps */
			fnext = __QSUB(fcurr, (q31_t)(((q63_t) gcurr * (*pk)) >> 31));
			gnext = __QADD(gcurr, (q31_t)(((q63_t) fnext * (*pk++)) >> 31));
			/* Output samples for last taps */
			acc += ((q63_t) gnext * *pv++);
			*px2++ = gnext;
			fcurr = fnext;

			tapCnt--;

		}

		/* y(n) += g0(n) * v0 */
		acc += (q63_t) fnext * (
		           *pv++);

		*px2++ = fnext;

		/* write out into pDst */
		*pDst++ = (q31_t)(acc >> 31u);

		/* Advance the state pointer by 4 to process the next group of 4 samples */
		pState = pState + 1u;
		blkCnt--;

	}

	/* Processing is complete. Now copy last S->numStages samples to start of the buffer
	   for the preperation of next frame process */

	/* Points to the start of the state buffer */
	pStateCurnt = &S->pState[0];
	pState = &S->pState[blockSize];

	tapCnt = numStages >> 2u;

	/* copy data */
	while(tapCnt > 0u) {
		*pStateCurnt++ = *pState++;
		*pStateCurnt++ = *pState++;
		*pStateCurnt++ = *pState++;
		*pStateCurnt++ = *pState++;

		/* Decrement the loop counter */
		tapCnt--;

	}

	/* Calculate remaining number of copies */
	tapCnt = (numStages) % 0x4u;

	/* Copy the remaining q31_t data */
	while(tapCnt > 0u) {
		*pStateCurnt++ = *pState++;

		/* Decrement the loop counter */
		tapCnt--;
	};

#else

	/* Run the below code for Cortex-M0 */
	/* Sample processing */
	while(blkCnt > 0u) {
		/* Read Sample from input buffer */
		/* fN(n) = x(n) */
		fcurr = *pSrc++;

		/* Initialize state read pointer */
		px1 = pState;
		/* Initialize state write pointer */
		px2 = pState;
		/* Set accumulator to zero */
		acc = 0;
		/* Initialize Ladder coeff pointer */
		pv = &S->pvCoeffs[0];
		/* Initialize Reflection coeff pointer */
		pk = &S->pkCoeffs[0];

		tapCnt = numStages;

		while(tapCnt > 0u) {
			gcurr = *px1++;
			/* Process sample */
			/* fN-1(n) = fN(n) - kN * gN-1(n-1) */
			fnext =
			    clip_q63_to_q31(((q63_t) fcurr -
			                     ((q31_t)(((q63_t) gcurr * (*pk)) >> 31))));
			/* gN(n) = kN * fN-1(n) + gN-1(n-1) */
			gnext =
			    clip_q63_to_q31(((q63_t) gcurr +
			                     ((q31_t)(((q63_t) fnext * (*pk++)) >> 31))));
			/* Output samples */
			/* y(n) += gN(n) * vN  */
			acc += ((q63_t) gnext * *pv++);
			/* write gN-1(n-1) into state for next sample processing */
			*px2++ = gnext;
			/* Update f values for next coefficient processing */
			fcurr = fnext;

			tapCnt--;
		}

		/* y(n) += g0(n) * v0 */
		acc += (q63_t) fnext * (
		           *pv++);

		*px2++ = fnext;

		/* write out into pDst */
		*pDst++ = (q31_t)(acc >> 31u);

		/* Advance the state pointer by 1 to process the next group of samples */
		pState = pState + 1u;
		blkCnt--;

	}

	/* Processing is complete. Now copy last S->numStages samples to start of the buffer
	   for the preperation of next frame process */

	/* Points to the start of the state buffer */
	pStateCurnt = &S->pState[0];
	pState = &S->pState[blockSize];

	tapCnt = numStages;

	/* Copy the remaining q31_t data */
	while(tapCnt > 0u) {
		*pStateCurnt++ = *pState++;

		/* Decrement the loop counter */
		tapCnt--;
	}

#endif /*   #ifndef ARM_MATH_CM0 */

}




/**
 * @} end of IIR_Lattice group
 */
